Low alloy high tensile strength high impact strength steel



Unite States Patent LOW ALLOY HIGH TENSILE STRENGTH HIGH IMPACT STRENGTH STEEL Carl M. Carman, Philadelphia, and Dominick F. Armiento, Huntingdon Valley, Pa., assignors to the United States of America as represented by the Secretary of the Army No Drawing. Filed Aug. 4, 195's, Ser. No. 753,164

2 Claims. (Cl. 148-36) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

This invention relates to a relatively low alloy steel, characterized by high impact strength and high hardenability after heat treatment to develop high strength and hardness, and has as an object to present a steel composition which has high impact strength at low temperatures and which withstands repeated reheating to 600 F. without a substantial loss in physical properties.

The need for reduced weight of ordnance material especially recoilless rifles and cannon to meet the increasing demand for mobility, has brought about the requirement for ultra high strength steels. The steel must have high strength, high toughness, high impact values at low temperatures and must not lose any substantial amount of these properties when subjected to repeated reheating, during firing cycles to about 600 F Recently, low alloy steels have been discovered which have high toughness, high tensile strength and hardness, and have found wide use in aircraft, automotive and railroad applications. These steels have V-notch Charpy bar impact strengths that are higher than the values expected in light of the straight line relationship of impact strength to Rockwell C hardness. That is, these new steels have high impact strengths-about 20-25 ft.-lbs., at high hardnesses--about Rockwell C 50, instead of the expected ft.-lbs. impact strength of other alloys. However, none of these improved steels have the combination of high tensile strength and high impact strength when subjected to repeated reheating to 600 F.

We have discovered that a low alloy manganese-chromium nickel-molybdenum-silicon-vanadium steel, as specified, below, overcomes the prior art difficulties, and is characterized by unusually high toughness at high tensile strengths and hardness, while at the same time maintaining these high values after repeated reheating to 600 F. In addition, there is no substantial reduction in impact strength at 1l0 F.

The chemical composition of our steel i as follows:

Percent Carbon About .30 to .35 Manganese About .75 to 1.00 Chromium About .70 to .90 Nickel About 1.50 to 2.00 Molybdenum About .40 to .60 Silicon About 1.25 to 1.75 Vanadium About .08 to .15

Table I gives the mechanical properties of a .34% carbon steel.

2 TABLE I Heat treatment [Oil quenched from 1625 F. and tempered at 600 F.] 5 Mechanical properties:

Hardness, Rockwell C Yield strength, p.s.i. (0.1% offset) 210,000 Tensile strength, p.s.i 225,000 Elongation in 2 inches, percent 11 Reduction in area, percent V-notch, Charpy-bar, impact values, ft.-

lbs.- 1

Tested at room temperature 25.4 Tested at 40 F 22.8 15 Tested -110 F 20.0

Table II shows the important new property of this steel-its ability to retain without any substantial loss, its mechanical properties, after ageing over a long period 0 achieved during any sustained firing of a recoilless rifle.

TABLE H Yield Tensile Elongation Reduction Time at 600 F. Strength Strength (In./In.- In Area (Hours) (.1% Off (p.s.i.) percent) (percent) set. p.s.l

In the appended claims, by the expression balance substantially all iron 'is meant iron except for impurities Within commercial tolerances, and other elements not to exceed in aggregate 1%, which elements do not affect the defined characteristics of the steel.

We claim:

1. A low alloy steel characterized by having a Charpy' notched impact resistance of at least about 20 foot-- 40 pounds at -110 F. and a tensile strength of at least about 220,000 p.s.i. after repeated reheating at 600 F., said steel having been heat treated by cooling sufficiently rapidly from an austenitizing temperature to obtain a martensitic structure and thereafter tempering Within 'the to 35% carbon, about .75 to 1.00% manganese, about .70 to .90% chromium, about 1.50 to 2.00% nickel, about .40 to .60% -molybdenum, about 1.25 to 1.75%

silicon and about .08 to .15% vanadium and the balance substantially all iron.

2. A low alloy steel, heat treated by cooling sufficiently rapidly from an austenitizing temperature to avoid high chromium, about 1.50 to 2.00% nickel, about .40 to,.60%

molybdenum, about 1.25 to 1.75 silicon and about .08

to .15% vanadium, and the balance substantially all'iron.

References Cited in the file of this patent 5 UNITED STATES PATENTS I 2,345,345 Bauscher .July 29, 19,587

OTHER REFERENCES I Steel, Metal Selection following page 162 in yolume 139, No. 14, October 1, 1956. I T

of time at 600 F. to simulate the temperature most I range of 550 to 650 F., said steel comprising about .30 A

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N016 2 959 506 November 8, 1960 Carl M, Carmen et a1;

It is hereby certified that error appears in the above numbered pat-" ent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 8, for "225,000" read 255,000

Signed and sealed this 8th day of January 1963.

(SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents 

1. A LOW ALLOY STEEL CHARACTERIZED BY HAVING A CHARPY NOTCHED IMPACT RESISTANCE OF AT LEAST ABOUT 20 FOOTPOUNDS AT -100*F. AND TENSILE STRENGTH OF AT LEAST ABOUT 220,000 P.S.I. AFTER REPEATED REHEATING AT 600*F., SAID STEEL HAVING BEEN HEATED BY COOLING SUFFICEINTLY RAPIDLY FROM AN AUSTENIZING TEMPERATURE TO OBTAIN A MARTENSTIC STRUCTURE AND THEREAFTER TEMPERING WITHIN THE RANGE OF 550 TO 650*F. SAID STEEL COMPRISING ABOUT .30 TO 35% CARBON, ABOUT .75 TO 1.00% MANGANESE, ABOUT .70 TO .90% CHRONUIM ABOUT 1.50 TO 2.00% NICKEL, ABOUT .40 TO .60% MOLYBDNUM, ABOUT 1.25 TO 1.75% SILICON AND ABOUT .08 TO 15% VANADIUM AND THE BALANCE SUBSTANTIALLY ALL IRON. 